This invention relates to composite elastic yarns and a process for making them. The invention is more particularly concerned with a composite of relatively inelastic filaments entangled around spandex elastic yarn or other highly elastic yarn.
Elastic yarns for textile use are usually covered with relatively inelastic filaments which may be any of the synthetic filaments commonly used for textile purposes. When used in combination with elastic yarns, such filaments may be designated as "hard fibers." The hard fibers are used to protect the elastic yarn from abrasion, to provide strength at the maximum useful extension of the composite yarn so that the elastic yarn will not be broken, and to provide lower running friction properties to improve the performance of the composite yarn in knitting or weaving operations. The hard fibers also make possible the production of fabrics having the appearance and feel of fabrics knitted or woven from conventional inelastic yarns.
The most common method of producing such composite yarns is to twist one or more yarns of hard fibers about the elastic yarn while the elastic yarn is extended to about the maximum extent desired for use in the final fabric. When one or more covering yarns are wrapped spirally in a single direction about an elastic yarn, the composite yarn is called a "single covered" elastic yarn. Such composite yarns have torque due to the unidirectional twist. When additional yarn or yarns are also wrapped around the composite yarn with opposite direction of twist, the result is called a "double covered" elastic yarn. Since a large number of spiral turns per yard of yarn are required for adequate covering of the elastic yarn, and the wrapping operation is slow, production of single or double covered elastic yarn is costly.
Composite yarns can be produced at higher speeds by false twisting a covering of hard fibers about an elastic yarn and heat setting the false twist in the hard fibers. A relatively loose covering of hard fibers having a reversing helical crimp can be produced in this way. Objectionable slippage of the covering over the elastic yarn can be avoided if the heat-setting treatment is performed at a temperature which causes portions of the hard fibers to adhere to the elastic yarn. However, heat-treatment of the elastic yarn is undesirable because it causes a serious reduction in elastic stretch properties.
Hard fiber coverings have also been applied to elastic yarns with bulking jets as disclosed in Marshall U.S. Pat. No. 3,078,654, Breen U.S. Pat. No. 3,013,379 and Miyasaka Japanese Application Pulication 40-21496/1965. Bulk is provided by crunodal or other loops which project from the surface even when the composite yarn is stretched to the maximum useful extension of the yarn. Projecting loops are undesirable when the composite yarn is extended under tensions used in knitting or weaving because the loops interfere with processing the yarn into fabric.
The present invention provides important improvements with respect to the above-mentioned problems. Other advantages of the invention will become apparent from the specification, drawings and claims.